Welcome to HVAC-Talk.com, a non-DIY site and the ultimate Source for HVAC Information & Knowledge Sharing for the industry professional! Here you can join over 150,000 HVAC Professionals & enthusiasts from around the world discussing all things related to HVAC/R. You are currently viewing as a NON-REGISTERED guest which gives you limited access to view discussions

To gain full access to our forums you must register; for a free account. As a registered Guest you will be able to:

Participate in over 40 different forums and search/browse from nearly 3 million posts.

I was led to believe these things understood defrost based upon temperature. Given the source of the contradiction, I had to dig. I guess pressure increase does not trigger defrost. What does is really not very clear to me but probably will be to you:

And in a mild climate where the btu cost of propane has a snowballs chance in hell of approaching the cost of high cop heat pump, having a few btu of electric resistance combined with the heat pump for a few hours a winter is going to be WAY WAY cheaper than paying the incremental on the furnace. Paying the additional cost of burning propane particularly when you factor the heat pump CAN run with the resistance (like an additional stage) and the propane CAN NOT.

I simply have not heard of 50c kwh electric, if it exists it's very rare, and that's still cheaper than propane at most temps.

Forward energy view is electric will become more and more closely tied to natural gas. The only source that can hold a candle to the btu cost of these high COP heat pumps is Natural Gas, and that requires some pretty cold temperatures. This is very likely to remain true for a long time.

On demand defrost uses the temp difference between the air and the liquid line to determine if there is ice/frost on the coil to a point that it needs to be defrosted. After the outdoor temp drops below X degrees(varies with manufacturer) they won't go into defrost except for once every 6 hours of compressor run time to make sure the outdoor coil doesn't become oil logged.

Carrier tries to mimic the efficiencies of on demand defrost. But misses the boat a bit. Its better then just time and temp defrost, but still activated by only coil temp and compressor run time(with respect to outdoor temp being under 50). But when its 10 degrees outside, Carriers Ideal will still do needless defrost cycles. On Demand won't.

I will be having a re-quote done on a 2 stage 10KW electric backup, removing the propane furnace. I suspect the capital cost will be pretty close as I will need to run a 60A service about 80' from the garage to the crawl space for the strips.

As pointed out, this will make the heat staging a little more complex as I will want to be able to stage Y, Y2, W and W2. Would the EcoBee EB-STAT-02 be a good candidate for this?

I will be having a re-quote done on a 2 stage 10KW electric backup, removing the propane furnace. I suspect the capital cost will be pretty close as I will need to run a 60A service about 80' from the garage to the crawl space for the strips.

As pointed out, this will make the heat staging a little more complex as I will want to be able to stage Y, Y2, W and W2. Would the EcoBee EB-STAT-02 be a good candidate for this?

I believe it would. I'm having great fun with mine. Putting 2 more in this weekend.

That said, the ability to truly communicate with the equipment is like the difference between a 1999 motorola flip phone and a droid razr maxx.

So if you get communicating equipment (ie Carrier or American Standard), get the manufacturers communicating thermostat.

Assuming equal cost,,, I would rather have a toaster oven with resistance heaters that last forever and a relatively simple control board in a unit that requires essentially no maintenance over a unit that has multiple pressure switches, gas valves, condensate drains, inducer motor, and igniters to fail and requires far more service. If you factor a 20yr lifespan my money says you will have far less invested in your system with electric backup.

Assuming equal cost,,, I would rather have a toaster oven with resistance heaters that last forever and a relatively simple control board in a unit that requires essentially no maintenance over a unit that has multiple pressure switches, gas valves, condensate drains, inducer motor, and igniters to fail and requires far more service. If you factor a 20yr lifespan my money says you will have far less invested in your system with electric backup.

Is there anywhere in the U.S. where you can get a Btu of heat from an electric heater for the same cost in energy as a Btu of heat from a gas furnace would cost?

Given his choices of propane or electric and using the rates provided it would be $3.13 a therm for propane and $3.22 a therm for electric. Based in the fact that the balance point is 30 degrees he will be using essentially all propane below 30 but with the heat pump he will be able to run the unit down to the design temp of 15 degrees with a cop of 2.75 (21200 but output) and supplement the balance of 12800 btus at essentially the same cost of propane. The big difference is that he will only need to heat 12800 btus at $3.22 and the 21200 btus at a bonus of $1.17 a therm instead of 34000
Btus at $3.13........If my math is correct......$1.09 per hour on propane and $.67 an hour on heatpump with electric backup. No brainier for me. Ass-u-me??? The verdict is still out